The present invention relates to a method of processing soybean by use of an enzyme, and particularly a method of processing soybean, which comprises the step of efficiently separating soybean cells from each other by use of a pectinase produced by microorganisms of the genus Bacillus. In addition, the present invention relates to a processed soybean obtained by the same method, and a food containing the processed soybean.
Soybean, which has been known as the xe2x80x9cmiracle cropxe2x80x9d, is a nutritious food material containing abundant vitamins and well-balanced protein, carbohydrate and lipid components. In particular, the quality of the soybean protein is so excellent that it is often called xe2x80x9cthe meat of the fieldxe2x80x9d.
Soybean also contains natural isoflavone. In recent years, isoflavone has gained public attention because it produces a similar action to female hormone, and is useful to reduce dissolution of calcium from the human body and to prevent rapidly increasing cases of osteoporosis. In addition, it is said that isoflavone has an effect of preventing menopausal disorder and cancer and improving their symptoms. Furthermore, the soybean contains such constituents as saponin, peptide and lecithin. It is said that these constituents are useful to prevent diseases attributable to habits in life (diseases common in adults).
However, since the soybean has a hard tissue, its digestion-absorption coefficient for the human body is low in case of eating boiled or roasted soybean. Therefore, a processed soybean is produced by mashing the soybean after heating to thereby improve the digestion-absorption coefficient. Well-known processed soybean foods available today include, for example, soybean milk obtained by mashing soybean, heating the mashed soybean and then performing a filtering operation, and tofu obtained by adding a protein coagulant to the soybean milk to coagulate nutritious constituents of the soybean milk together with the protein. In addition, soybean oil can be obtained by extracting oil and fat from the soybean.
Thus, improving the digestion-absorption coefficient by the processed soybean foods has made it possible to eat soybean while enjoying various tastes and feelings of eating. However, water-soluble proteins and emulsified oil and fat of soybean are mainly used to obtain the soybean milk and tofu. The residue of soybean is thrown away as okara (strained draff weighing about 30 to 50% of raw soybean). In addition, only 20% of soybean is used as the soybean oil, and the remaining soybean cake is used almost entirely as animal feeds and fertilizers. In the future, it is predicted that food shortages become more serious. Therefore, developing a method of processing the whole of soybean as food material will be a countermeasure for the predicted food shortages.
In the past, efforts have been made to use a soybean powder obtained by mechanically pulverizing soybean or soybean cake. However, since soybean cells are destroyed during the pulverizing operation, the soybean powder has a smell characteristic to soybean. Due to this smell, even when the soybean powder is used together with other foods, original tastes of the foods are deteriorated. This limits the scope of its application and the amounts added as a food ingredient. Although soybean proteins extracted from soybean cake are often used for processed foods, the application is limited due to the soybean smell, too. Consequently, soybean cake is used almost entirely as animal feeds and fertilizers under the present circumstances.
For example, Japanese Patent Early Publication [KOKAI] No. 61-219347 discloses a decomposed product of soybean and its production method. This method comprises the steps of pulverizing soybean, adding water to the pulverized soybean to obtain a slurry, heating the slurry at a temperature from 60xc2x0 C. to 100xc2x0 C. for a time period of 5 to 180 minutes, homogenizing the heated slurry under high pressure (100 to 800 kg/cm2), and hydrolyzing a resultant homogenate with a neutral protease (enzyme capable of breaking a peptide bond between protein and peptide) produced by the Bacillus subtilis. After a resultant hydrolyzate is heated and maintained for a required time period to inactivate the enzyme action, it is dried by way of spray drying to obtain the decomposed product of the soybean.
According to this method, the entire constituents of soybean can be used, and the digestion-absorption coefficient for the human body can be improved. However, since the soybean cells are destroyed during the pulverizing step and the homogenizing treatment performed under the high pressure, there is a problem that the characteristic soybean smell originating from intracellular constituents remains in the decomposed product.
On the other hand, Japanese Patent Early Publication [KOKAI] No. 8-89197 discloses a method of producing a processed soybean food such as soybean milk. This method comprises the steps of adding water to soybean, keeping the soybean at room temperature for a required time period, adding a protopectinase to the soybean to obtain a mixture, holding this mixture at room temperature (for example, 28xc2x0 C.) for a long time period (for example, 8 hours) while agitating the mixture to achieve an enzyme treatment, and then filtrating the soybean from the mixture to obtain the soybean milk. It is also described that a mixture of protopectinase and pectinesterase, pectin-polygalacturonase or polygalacturonase may be used for the enzyme treatment.
According to this method, it is possible to separate soybean cells from each other without destroying the soybean cells. Each of the separated soybean cells maintains a state of enveloping nutritious constituents such as proteins and fat in the cell wall. Therefore, the problem of the characteristic soybean smell originating from the intracellular constituents can be solved. However, the enzyme treatment for separating the soybean cells from each other has not necessarily been sufficient for reasons stated below. Since the enzyme treatment using the aforementioned enzyme is performed at room temperature, there is a problem that various germs easily propagate to induce the occurrence of smell and bubbles by fermentation. In addition, since the time required for the enzyme treatment is extremely long, there is a problem that the production efficiency is too low for industrial applications.
Japanese Patent Publication No. 42-22169 discloses a method of producing an easily dispersible powder food from beans. This method comprises the steps of adding a protopectinase produced by microorganisms of the genus Rhizopus to soybean previously soaked in water to perform an enzyme treatment, separating the treated soybean by filtration, and drying the separated soybean by a freeze drying method to obtain the powder food. It is also described that a protopectinase produced by microorganisms of the genus Aspergillus or Penicillium may be used for the enzyme treatment.
However, this method has substantially the same problems that were described above with reference to Japanese Patent Early Publication [KOKAI] No. 8-89197.
In consideration of the above problems, a primary object of the present invention is to provide a method of processing soybean by use of an enzyme, which is capable of efficiently producing a processed soybean food having substantially no smell characteristic to the soybean and an improved digestion-absorption coefficient for the human body by using the entire constituents of the soybean. The processing method of the present invention is characterized by the following steps. That is, the soybean is soaked in water, and then heated in the presence of water. After the heated soybean is cooled, an enzyme treatment is performed by adding water and a pectinase produced by microorganisms of the genus Bacillus to the soybean to obtain a first mixture, and holding the first mixture for a predetermined time period while agitating the first mixture to thereby obtain a slurry, in which single cells of the soybean are dispersed. After the enzyme treatment, the pectinase is inactivated. Next, a second mixture is prepared by mixing the slurry with a powder obtained by processing a pulse other than the soybean. The second mixture is dried by a flash drying or spray drying method to obtain a processed soybean powder.
The above-described method of the present invention presents the following advantages.
1. By use of the pectinase produced by the microorganisms of the genus Bacillus, the soybean cells can be separated from each other in a very short time as compared to the conventional case. In addition, the separated soybean cells are characterized in that damages to cell membranes and cell walls are small, and protein bodies and lipid bodies are stably maintained in the interior of each of the separated soybean cells. Thus, it is possible to provide the separated soybean cells of high quality.
2. Since the enzyme treatment can be performed at a high temperature of about 60xc2x0 C. by use of the pectinase produced by the microorganisms of the genus Bacillus, it is possible to prevent the propagation of various germs as compared to the enzyme treatment using an enzyme produced by microorganisms of the genus Rhizopus or the like. Therefore, the enzyme treatment is advantageous in obtaining fresh soybean single cells. Additionally, since the pectinase shows a high enzyme activity in a range from neutrality to low alkalinity, i.e., a pH range of 7 to 8, it is possible to perform the enzyme treatment without using a pH-controlling agent.
3. By combination of the step of preparing the second mixture by mixing the slurry with the powder obtained by processing the pulse other than the soybean and the step of drying the second mixture by the flash drying or spray drying method, it is possible to produce the processed soybean powder having substantially no smell characteristic to the soybean and uniform quality without giving damages to the separated soybean cells.
Another object of the present invention is to provide a method of processing soybean by use of an enzyme, which is characterized by the following steps. That is, the soybean is soaked in water, and then heated in the presence of water. After the heated soybean is cooled, an enzyme treatment is performed by adding water and a pectinase produced by microorganisms of the genus Bacillus to the soybean to obtain a mixture, and holding the mixture for a predetermined time period while agitating the mixture. After the enzyme treatment, the pectinase is inactivated to thereby obtain a processed soybean liquid, in which single cells of the soybean are dispersed. Therefore, the present invention is useful for providing the processed soybean liquid as well as the processed soybean powder.
A further object of the present invention is to provide a processed food produced by adding the processed soybean powder or the processed soybean liquid obtained by the present method to a food ingredient.
These and other objects and advantages will become apparent from the following detailed description of the preferred embodiments and examples of the invention.